U.S. patent application number 15/600066 was filed with the patent office on 2017-11-30 for magnetoresistive effect device.
This patent application is currently assigned to TDK CORPORATION. The applicant listed for this patent is TDK CORPORATION. Invention is credited to Tetsuya SHIBATA, Tsuyoshi SUZUKI, Junichiro URABE, Takekazu YAMANE.
Application Number | 20170345449 15/600066 |
Document ID | / |
Family ID | 60418269 |
Filed Date | 2017-11-30 |
United States Patent
Application |
20170345449 |
Kind Code |
A1 |
SHIBATA; Tetsuya ; et
al. |
November 30, 2017 |
MAGNETORESISTIVE EFFECT DEVICE
Abstract
A magnetoresistive effect device includes a magnetoresistive
effect element first and second ports, a signal line, an inductor,
and a direct current input terminal. The first port, the
magnetoresistive effect element, and the second port are connected
in series in this order via the signal line. The inductor is
connected to one of the signal line between the magnetoresistive
effect element and the first port and the signal line between the
magnetoresistive effect element and the second port and is capable
of being connected to ground. The direct-current input terminal is
connected to the other of the above signal lines. A closed circuit
including the magnetoresistive effect element, the signal line, the
inductor, the ground, and direct-current input terminal is capable
of being formed. The magnetoresistive effect element is arranged so
that direct current flows in a direction from a magnetization fixed
layer to a magnetization free layer.
Inventors: |
SHIBATA; Tetsuya; (Tokyo,
JP) ; URABE; Junichiro; (Tokyo, JP) ; YAMANE;
Takekazu; (Tokyo, JP) ; SUZUKI; Tsuyoshi;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TDK CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
TDK CORPORATION
Tokyo
JP
|
Family ID: |
60418269 |
Appl. No.: |
15/600066 |
Filed: |
May 19, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 33/1284 20130101;
H01L 43/00 20130101; G01R 33/00 20130101; G01R 33/093 20130101;
H03H 2/00 20130101; G11B 5/3945 20130101 |
International
Class: |
G11B 5/39 20060101
G11B005/39 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2016 |
JP |
2016-103900 |
Feb 15, 2017 |
JP |
2017-026216 |
Claims
1. A magnetoresistive effect device comprising: at least one
magnetoresistive effect element including a magnetization fixed
layer, a magnetization free layer, and a spacer layer arranged
between the magnetization fixed layer and the magnetization free
layer; a first port through which a high-frequency signal is input;
a second port through which a high-frequency signal is output; a
signal line; an inductor or a resistance element; and a
direct-current input terminal, wherein the first port, the
magnetoresistive effect element, and the second port are connected
in series in this order via the signal line, wherein the inductor
or the resistance element is connected to one of the signal line
between the magnetoresistive effect element and the first port and
the signal line between the magnetoresistive effect element and the
second port and is capable of being connected to ground, wherein
the direct-current input terminal is connected to the other of the
signal line between the magnetoresistive effect element and the
first port and the signal line between the magnetoresistive effect
element and the second port, wherein a closed circuit including the
magnetoresistive effect element, the signal line, the inductor, the
ground and direct-current input terminal or a closed circuit
including the magnetoresistive effect element, the signal line, the
resistance element, the ground, and direct-current input terminal
is capable of being formed, and wherein the magnetoresistive effect
element is arranged so that direct current supplied from the
direct-current input terminal flows through the magnetoresistive
effect element in a direction from the magnetization fixed layer to
the magnetization free layer.
2. The magnetoresistive effect device according to claim 1, further
comprising; at least one frequency setting mechanism capable of
setting a spin torque resonance frequency of the magnetoresistive
effect element.
3. The magnetoresistive effect device according to claim 2, wherein
the frequency setting mechanism is an effective magnetic field
setting mechanism capable of setting an effective magnetic field in
the magnetization free layer and is capable of varying the spin
torque resonance frequency of the magnetoresistive effect element
by varying the effective magnetic field.
4. The magnetoresistive effect device according to claim 1, wherein
the at least one magnetoresistive effect element includes a
plurality of magnetoresistive effect elements having different spin
torque resonance frequencies, and wherein the magnetoresistive
effect elements are connected in parallel to each other.
5. The magnetoresistive effect device according to claim 2, wherein
the at least one magnetoresistive effect element includes a
plurality of magnetoresistive effect elements, wherein the
magnetoresistive effect elements are connected in parallel to each
other, and wherein the at least one frequency setting mechanism
includes a plurality of frequency setting mechanisms so that the
spin torque resonance frequencies of the magnetoresistive effect
elements are capable of being individually set.
6. The magnetoresistive effect device according to claim 1, wherein
the at least one magnetoresistive effect element includes a
plurality of magnetoresistive effect elements having different spin
torque resonance frequencies, and wherein the magnetoresistive
effect elements are connected in series to each other.
7. The magnetoresistive effect device according to claim 2, wherein
the at least one magnetoresistive effect element includes a
plurality of magnetoresistive effect elements, wherein the
magnetoresistive effect elements are connected in series to each
other, and wherein the at least one frequency setting mechanism
includes a plurality of frequency setting mechanisms so that the
spin torque resonance frequencies of the magnetoresistive effect
elements are capable of being individually set.
8. The magnetoresistive effect device according to claim 4, wherein
plan view shapes of the magnetoresistive effect elements having
different spin torque resonance frequencies are different from each
other in aspect ratio.
9. The magnetoresistive effect device according to claim 6, wherein
plan view shapes of the magnetoresistive effect elements having
different spin torque resonance frequencies are different from each
other in aspect ratio.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a magnetoresistive effect
device including a magnetoresistive effect element.
2. Description of the Related Art
[0002] The speed of wireless communication has increased in recent
years with the increasing functions of mobile communication
terminals, such as mobile phones. Since the communication speed is
proportional to the band width of frequencies that are used, the
number of frequency bands necessary for communication is increased.
Accordingly, the number of high-frequency filters that are mounted
in mobile communication terminals is increased. Spintronics has
been studied in recent years as a field that is probably applicable
to new high-frequency components. One phenomenon that has received
attention is the spin torque resonance phenomenon, which is caused
by a magnetoresistive effect element (refer to Nature, Vol. 438,
No. 7066, pp. 339 to 342 17 Nov. 2005). Application of alternating
current to a magnetoresistive effect element causes spin torque
resonance in the magnetoresistive effect element, and the
resistance value of the magnetoresistive effect element oscillates
with a fixed cycle at a frequency corresponding to a spin torque
resonance frequency. The spin torque resonance frequency of the
magnetoresistive effect element varies with the strength of the
magnetic field applied to the magnetoresistive effect element. The
spin torque resonance frequency of the magnetoresistive effect
element is generally within a high-frequency band from several
gigahertz to several tens of gigahertz.
SUMMARY OF THE INVENTION
[0003] Although the magnetoresistive effect element may be applied
to a high-frequency device utilizing the spin torque resonance
phenomenon, specific configurations to apply the magnetoresistive
effect element to a high-frequency device, such as a high-frequency
filter, have not been proposed. Accordingly, the present invention
aims to provide a magnetoresistive effect device capable of
realizing a high-frequency device, such as a high-frequency filter,
which includes a magnetoresistive effect element.
[0004] A magnetoresistive effect device according to an embodiment
of the present invention includes at least one magnetoresistive
effect element including a magnetization fixed layer, a
magnetization free layer, and a spacer layer arranged between the
magnetization fixed layer and the magnetization free layer; a first
port through which a high-frequency signal is input; a second port
through which a high-frequency signal is output; a signal line; an
inductor or a resistance element; and a direct-current input
terminal. The first port, the magnetoresistive effect element, and
the second port are connected in series in this order via the
signal line. The inductor or the resistance element is connected to
one of the signal line between the magnetoresistive effect element
and the first port and the signal line between the magnetoresistive
effect element and the second port and is capable of being
connected to ground. The direct-current input terminal is connected
to the other of the signal line between the magnetoresistive effect
element and the first port and the signal line between the
magnetoresistive effect element and the second port. A closed
circuit including the magnetoresistive effect element, the signal
line, the inductor, the ground, and direct-current input terminal
or a closed circuit including the magnetoresistive effect element,
the signal line, the resistance element, the ground, and
direct-current input terminal is capable of being formed. The
magnetoresistive effect element is arranged so that direct current
supplied from the direct-current input terminal flows through the
magnetoresistive effect element in a direction from the
magnetization fixed layer to the magnetization free layer.
[0005] With the above magnetoresistive effect device, the input of
the high-frequency signal from the first port to the
magnetoresistive effect element via the signal line enables spin
torque resonance to be induced in the magnetoresistive effect
element. Due to the direct current flowing through the
magnetoresistive effect element in the direction from the
magnetization fixed layer to the magnetization free layer
simultaneously with the spin torque resonance, the element
impedance of the magnetoresistive effect element at a frequency
equal to the spin torque resonance frequency is increased. The
series connection of the first port, the magnetoresistive effect
element, and the second port through which a high-frequency signal
is output in this order enables the high-frequency signal to be
passed at a non-resonant frequency at which the magnetoresistive
effect element is in a low impedance state and to be cut off at a
resonant frequency at which the magnetoresistive effect element is
in a high impedance state. In other words, the magnetoresistive
effect device is capable of having frequency characteristics as a
high-frequency filter.
[0006] The direct current supplied from the direct-current input
terminal flows through the closed circuit including the
magnetoresistive effect element, the signal line, the inductor, the
ground, and the direct-current input terminal or the closed circuit
including the magnetoresistive effect element, the signal line, the
resistance element, the ground, and direct-current input terminal.
The closed circuit enables the direct current to be efficiently
applied to the magnetoresistive effect element. Since the
application of the direct current increases the amount of change in
element impedance of the magnetoresistive effect element, the
magnetoresistive effect device may function as a high-frequency
filter having a wide range of cut-off characteristics and bandpass
characteristics.
[0007] The magnetoresistive effect device preferably further
includes at least one frequency setting mechanism capable of
setting a spin torque resonance frequency of the magnetoresistive
effect element.
[0008] Since the spin torque resonance frequency of the
magnetoresistive effect element is capable of being set to an
arbitrary value in the above magnetoresistive effect device, the
magnetoresistive effect device may function as a filter having art
arbitrary frequency band.
[0009] In the magnetoresistive effect device, the frequency setting
mechanism may be an effective magnetic field setting mechanism
capable of setting an effective magnetic field in the magnetization
free layer and may be capable of varying the spin torque resonance
frequency of the magnetoresistive effect element by varying the
effective magnetic field.
[0010] With the above magnetoresistive effect device, since the
spin torque resonance frequency of the magnetoresistive effect
element is capable of being variably controlled, the
magnetoresistive effect device may function as a frequency variable
filter.
[0011] In the magnetoresistive effect device, the at least one
magnetoresistive effect element may include multiple
magnetoresistive effect elements having different spin torque
resonance frequencies, and the multiple magnetoresistive effect
elements may be connected in parallel to each other.
[0012] With the above magnetoresistive effect device, since the
multiple magnetoresistive effect elements having different spin
torque resonance frequencies are connected in parallel to each
other, a cutoff frequency band having a certain width is
provided.
[0013] In the magnetoresistive effect device, the at least one
magnetoresistive effect element may include multiple
magnetoresistive effect elements, the multiple magnetoresistive
effect elements may be connected in parallel to each other, and the
at least one frequency setting mechanism may include multiple
frequency setting mechanisms so that the spin torque resonance
frequencies of the multiple magnetoresistive effect elements are
capable of being individually set.
[0014] With the above magnetoresistive effect device, since the
multiple frequency setting mechanisms are provided so as to
individually set the spin torque resonance frequencies of the
multiple magnetoresistive effect devices, the spin torque resonance
frequencies of the respective magnetoresistive effect elements are
capable of being individually controlled. In addition, since the
multiple magnetoresistive effect elements are connected in parallel
to each other, a cutoff frequency band having a certain width is
provided.
[0015] In the magnetoresistive effect device, the at least one
magnetoresistive effect element may include multiple
magnetoresistive effect elements having different spin torque
resonance frequencies, and the multiple magnetoresistive effect
elements may be connected in series to each other.
[0016] With the above magnetoresistive effect device, since the
multiple magnetoresistive effect elements having different spin
torque resonance frequencies are connected in series to each other,
a cutoff frequency band having a certain width is provided.
[0017] In the magnetoresistive effect device, the at least one
magnetoresistive effect element may include multiple
magnetoresistive effect elements, the multiple magnetoresistive
effect elements may be connected in series to each other, and the
at least one frequency setting mechanism may include multiple
frequency setting mechanisms so that the spin torque resonance
frequencies of the multiple magnetoresistive effect elements are
capable of being individually set.
[0018] With the above magnetoresistive effect device, since the
multiple frequency setting mechanisms are provided so as to
individually set the spin torque resonance frequencies of the
multiple magnetoresistive effect devices, the spin torque resonance
frequencies of the respective magnetoresistive effect elements are
capable of being individually controlled. In addition, since the
multiple magnetoresistive effect elements are connected in series
to each other, a cutoff frequency band having a certain width is
provided.
[0019] In the magnetoresistive effect device, the plan view shapes
of the multiple magnetoresistive effect elements having different
spin torque resonance frequencies may be different from each other
in aspect ratio. "The plan view shape" means the shape of each of
the magnetoresistive effect elements when the magnetoresistive
effect element is viewed from above a plane perpendicular to the
stacking direction of the respective layers composing the
magnetoresistive effect element. "The aspect ratio" means the ratio
of the length of the long sides to the length of the short sides of
a rectangle circumscribed around the plan view shape of the
magnetoresistive effect element with a minimum area.
[0020] With the above magnetoresistive effect device, since the
plan view shapes of the multiple magnetoresistive effect elements
having different spin torque resonance frequencies have different
aspect ratios from each other, it is possible to manufacture the
multiple magnetoresistive effect elements having different spin
torque resonance frequencies from each other through the same
process. Specifically, since the multiple magnetoresistive effect
elements have the same film structure in the magnetoresistive
effect device, it is possible to collectively form the films of the
layers composing the multiple magnetoresistive effect elements.
[0021] According to the embodiment of the present invention, it is
possible to provide a magnetoresistive effect device capable of
realizing a high-frequency device, such as a high-frequency filter,
which includes a magnetoresistive effect element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic cross-sectional view of a
magnetoresistive effect device according to a first embodiment.
[0023] FIG. 2 is a graph illustrating the relationship between
frequency and attenuation for direct current in the
magnetoresistive effect device according to the first
embodiment.
[0024] FIG. 3 is a graph illustrating the relationship between
frequency and attenuation for the strength of a magnetic field in
the magnetoresistive effect device according to the first
embodiment.
[0025] FIG. 4 is a schematic cross-sectional view of a
magnetoresistive effect device according to a second
embodiment.
[0026] FIG. 5 is a top view of the magnetoresistive effect device
according to the second embodiment.
[0027] FIG. 6 is a graph illustrating the relationship between
frequency and attenuation in the magnetoresistive effect device
according to the second embodiment.
[0028] FIG. 7 is a schematic cross-sectional view of a
magnetoresistive effect device according to a third embodiment.
[0029] FIG. 8 is a graph illustrating the relationship between
frequency and attenuation in the magnetoresistive effect device
according to the third embodiment.
[0030] FIG. 9 is a schematic cross-sectional view of a
magnetoresistive effect device according to a fourth
embodiment.
[0031] FIG. 10 is a top view of the magnetoresistive effect device
according to the fourth embodiment.
[0032] FIG. 11 is a graph illustrating the relationship between
frequency and attenuation in the magnetoresistive effect device
according to the fourth embodiment.
[0033] FIG. 12 is a schematic cross-sectional view of a
magnetoresistive effect device according to a fifth embodiment.
[0034] FIG. 13 is a graph illustrating the relationship between
frequency and attenuation in the magnetoresistive effect device
according to the fifth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Embodiments of the present invention will herein be
described in detail with reference to the attached drawings. The
present invention is not limited by the content described in the
following embodiments. Components described below include
components easily supposed by persons skilled in the art,
components substantially equivalent to each other, and components
within an equivalent range. In addition, the components described
below may be appropriately combined with each other. Furthermore,
the components may be omitted, replaced, or modified without
departing from the true spirit and scope of the invention.
First Embodiment
[0036] FIG. 1 is a schematic cross-sectional view of a
magnetoresistive effect device 100 according to a first embodiment
of the present invention. The magnetoresistive effect device 100
includes a magnetoresistive effect element 1a, an upper electrode
5, a lower electrode 6, a first port 9a, a second port 9b, a signal
line 7, an inductor 10, a direct-current input terminal 11, and a
magnetic-field applying mechanism 12 serving as a frequency setting
mechanism. The magnetoresistive effect element 1a includes a
magnetization fixed layer 2, a spacer layer 3, and a magnetization
free layer 4. The first port 9a, the magnetoresistive effect
element 1a, and the second port 9b are connected in series in this
order via the signal line 7. The inductor 10 is connected to the
signal line 7 between the magnetoresistive effect element 1a and
the second port 9b (one of the signal line 7 between the
magnetoresistive effect element 1a and the first port 9a and the
signal line 7 between the magnetoresistive effect element 1a and
the second port 9b) and is capable of being connected to ground 8
via a reference voltage terminal 20. The direct-current input
terminal 11 is connected to the signal line 7 between the
magnetoresistive effect element 1a and the first port 9a (the other
of the signal line 7 between the magnetoresistive effect element 1a
and the first port 9a and the signal line 7 between the
magnetoresistive effect element 1a and the second port 9b). In
other words, the direct-current input terminal 11 is connected to
the signal line 7 at the opposite side to the inductor 10 with the
magnetoresistive effect element 1a in between the direct-current
input terminal 11 and the inductor 10. A closed circuit including
the magnetoresistive effect element 1a, the signal line 7, the
inductor 10, the ground 8, and the direct-current input terminal 11
is capable of being formed when the magnetoresistive effect device
100 is connected to the ground 8. More specifically, in the
magnetoresistive effect device 100, the connection of the inductor
10 to the ground 8 via the reference voltage terminal 20 and the
connection of a direct-current source 13 connected to the ground 8
to the direct-current input terminal 11 enable the closed circuit
including the magnetoresistive effect element 1a, the signal line
7, the inductor 10, the ground 8, and the direct-current input
terminal 11 to be formed.
[0037] The first port 9a is an input port through which a
high-frequency signal, which is an alternating current signal, is
input and the second port 9b is an output port through which a
high-frequency signal is output. The high-frequency signal input
through the magnetoresistive effect element 1a and the
high-frequency signal output through the second port 9b are, for
example, signals having frequencies of 100 MHz or more. The signal
line 7 is electrically connected to the magnetoresistive effect
element 1a via the upper electrode 5 and the lower electrode 6 so
as to sandwich the magnetoresistive effect element 1a between the
upper electrode 5 and the lower electrode 6. The high-frequency
signal input through the first port 9a flows through the
magnetoresistive effect element 1a and is supplied to the second
port 9b. Attenuation (S21), which is a dB value of a power ratio
(output power/input power) when the high-frequency signal is
supplied from the first port 9a to the second port 9b, is capable
of being measured with a high-frequency measuring device, such as a
network analyzer.
[0038] The upper electrode 5 and the lower electrode 6 serve as a
pair of electrodes and are disposed in the stacking direction of
the respective layers composing the magnetoresistive effect element
1a with the magnetoresistive effect element 1a in between the upper
electrode 5 and the lower electrode 6. Specifically, the upper
electrode 5 and the lower electrode 6 function as a pair of
electrodes to cause a signal (current) to flow through the
magnetoresistive effect element 1a in a direction intersecting with
the face of each layer composing the magnetoresistive effect
element 1a, for example, in a direction (stacking direction)
perpendicular to the face of each layer composing the
magnetoresistive effect element 1a. Each of the upper electrode 5
and the lower electrode 6 is preferably composed of a film made of
Ta, Cu, Au, AuCu, or Ru or a film made of two or more of the above
materials. One end (at the magnetization fixed layer 2 side) of the
magnetoresistive effect element 1a is electrically connected to the
signal line 7 via the upper electrode 5 and the other end (at the
magnetization free layer 4 side) of the magnetoresistive effect
element 1a is electrically connected to the signal line 7 via the
lower electrode 6.
[0039] The ground 8 functions as reference voltage. The shape of
the signal line with the ground 8 is preferably of a micro strip
line (MSL) type or a coplanar waveguide (CPW) type. In design of
the micro strip line shape or the coplanar waveguide shape,
designing the width of the signal line 7 and the distance to the
ground so that the characteristic impedance of the signal line 7 is
equal to the impedance of a circuit system enables the transmission
loss through the signal line 7 to be reduced.
[0040] The inductor 10 is connected between the signal line 7 and
the ground 8 and has a function to cut off high-frequency
components of the current and pass direct-current components of the
current with its inductance component. The inductor 10 may be a
chip inductor or an inductor composed of a pattern line.
Alternatively, the inductor 10 may be a resistance element having
an inductance component. The inductor 10 preferably has an
inductance value of 10 nH or more. The use of the inductor 10
enables direct current applied from the direct-current input
terminal 11 to flow through the closed circuit including the
magnetoresistive effect element 1a, the signal line 7, the inductor
10, the ground 8, and the direct-current input terminal 11 without
degrading the characteristics of the high-frequency signal passing
through the magnetoresistive effect element 1a.
[0041] The direct-current input terminal 11 is connected to the
signal line 7 at the opposite side to the inductor 10 with the
magnetoresistive effect element 1a in between the direct-current
input terminal 11 and the inductor 10. More specifically, the
direct-current input terminal 11 is connected to the signal line 7
between the magnetoresistive effect element 1a and the first port
9a. The connection of the direct-current source 13 to the
direct-current input terminal 11 enables the direct current to be
applied to the magnetoresistive effect element 1a. The
magnetoresistive effect element 1a is arranged so that the direct
current supplied from the direct-current input terminal 11 flows
through the magnetoresistive effect element 1a in a direction from
the magnetization fixed layer 2 to the magnetization free layer 4.
An inductor or a resistance element for cutting off the
high-frequency signal may be connected in series between the
direct-current input terminal 11 and the direct-current source
13.
[0042] The direct-current source 13 is connected to the ground 8
and the direct-current input terminal 11 and applies the direct
current from the direct-current input terminal 11 to the closed
circuit including the magnetoresistive effect element 1a, the
signal line 7, the inductor 10, the ground 8, and the
direct-current input terminal 11. The direct-current source 13 is
composed of, for example, a circuit in which a variable resistor is
combined with a direct-current voltage source and is capable of
varying the current value of the direct current. The direct-current
source 13 may be composed of a circuit which is capable of
generating constant direct current and in which a fixed resistor is
combined with a direct-current voltage source.
[0043] The magnetic-field applying mechanism 12 is disposed near
the magnetoresistive effect element 1a and applies a magnetic field
to the magnetoresistive effect element 1a to enable setting of a
spin torque resonance frequency of the magnetoresistive effect
element 1a. For example, the magnetic-field applying mechanism 12
is of an electromagnetic type or a strip line type capable of
variably controlling the strength of the applied magnetic field
using voltage or current. Alternatively, the magnetic-field
applying mechanism 12 may be a combination of the electromagnetic
type or the strip line type with a permanent magnet that supplies
only a constant magnetic field. In addition, the magnetic-field
applying mechanism 12 varies an effective magnetic field in the
magnetization free layer 4 by varying the magnetic field to be
applied to the magnetoresistive effect element 1a to enable the
spin torque resonance frequency Of the magnetoresistive effect
element 1a to be varied.
[0044] The magnetization fixed layer 2 is made of a ferromagnetic
material and the magnetization direction of the magnetization fixed
layer 2 is substantially fixed to one direction. The magnetization
fixed layer 2 is preferably made of a material having high spin
polarizability, such as Fe, Co, Ni, an alloy of Ni and Fe, an alloy
of Fe and Co, or an alloy of Fe, Co, and B. This achieves a high
magnetoresistive change rate. The magnetization fixed layer 2 may
be made of a Heusler alloy. The magnetization fixed layer 2
preferably has a film thickness or 1 nm to 10 nm. An
antiferromagnetic layer may be added so as to be in contact with
the magnetization fixed layer 2 in order to fix the magnetization
of the magnetization fixed layer 2. Alternatively, the
magnetization of the magnetization fixed layer 2 may be fixed using
magnetic anisotropy caused by the crystal structure of the
magnetization fixed layer 2 or the shape thereof. The
antiferromagnetic layer may be made of FeO, CoO, NiO, CuFeS.sub.2,
IrMn, FeMn, PtMn, Cr, or Mn.
[0045] The spacer layer 3 is arranged between the magnetization
fixed layer 2 and the magnetization free layer 4. The magnetization
of the magnetization fixed layer 2 and the magnetization of the
magnetization free layer 4 interact with each other to achieve the
magnetoresistive effect. The spacer layer 3 may be formed of a
layer made of a conductive material, an insulating material, or a
semiconductor material. Alternatively, the spacer layer 3 may be
formed of a layer in which a current flow point composed of a
conductor is included in an insulator.
[0046] When a non-magnetic conductive material is used for the
spacer layer 3, the non-magnetic conductive material may be Cu, Ag,
Au, or Ru. In this case, a giant magnetoresistive (GMR) effect is
produced in the magnetoresistive effect element 1a. When the GMR
effect is used, the spacer layer 3 preferably has a film thickness
of about 0.5 nm to 3.0 nm.
[0047] When a non-magnetic insulating material is used for the
spacer layer 3, the non-magnetic insulating material may be
Al.sub.2O.sub.3 or MgO. In this case, a tunnel magnetoresistive
(TMR) effect is produced in the magnetoresistive effect element 1a.
Adjusting the film thickness of the spacer layer 3 so that a
coherent tunnel effect is produced between the magnetization fixed
layer 2 and the magnetization free layer 4 achieves a high
magnetoresistive change rate. When the TMR effect is used, the
spacer layer 3 preferably has a film thickness of about 0.5 nm to
3.0 nm.
[0048] When a non-magnetic semiconductor material is used for the
spacer layer 3, the non-magnetic semiconductor material may be SnO,
In.sub.2O.sub.3, SnO.sub.2, ITO, GaO.sub.x, or Ga.sub.2O.sub.x. The
spacer layer 3 preferably has a film thickness of about 1.0 nm to
4.0 nm.
[0049] When a layer in which the current flow point composed of a
conductor is included in a non-magnetic insulator is used as the
spacer layer 3, the spacer layer 3 preferably has a structure in
which the current flow point composed of a conductor made of, for
example, CoFe, CoFeB, CoFeSi, CoMnGe, CoMnSi, CoMnAl, Fe, Co, Au,
Cu, Al, or Mg is included in the non-magnetic insulator made of
Al.sub.2O.sub.3 or MgO. In this case, the spacer layer 3 preferably
has a film thickness of about 0.5 nm to 2.0 nm.
[0050] The direction of the magnetization of the magnetization free
layer 4 is capable of being varied. The magnetization free layer 4
is made of a ferromagnetic material. The direction of the
magnetization of the magnetization free layer 4 is capable of being
varied with, for example, an externally applied magnetic field or
spin polarized electrons. When the magnetization free layer 4 is
made of a material having a magnetic easy axis in an in-plane
direction, the material may be, for example, CoFe, CoFeB, CoFeSi,
CoMnGe, CoMnSi, or CoMnAl. The magnetization free layer 4
preferably has a film thickness of about 1 nm to 30 nm. When the
magnetization free layer 4 is made of a material having the
magnetic easy axis in a plane normal direction, the material may
be, for example, Co, a CoCr-based alloy, a Co multilayer film, a
CoCrPt-based alloy, an FePt-based alloy, an SmCo-based alloy
including rare earth, or a TbFeCo alloy. The magnetization free
layer 4 may be made of a Heusler alloy. A material having high spin
polarizability may be disposed between the magnetization free layer
4 and the spacer layer 3. This achieves a high magnetoresistive
change rate. The material having a high spun polarizability may be,
for example, a CoFe alloy or a CoFeB alloy. Each of the CoFe alloy
and the CoFeB alloy preferably has a film thickness of about 0.2 nm
to 1.0 nm.
[0051] A cap layer, a seed layer, or a buffer layer may be disposed
between the upper electrode 5 and the magnetoresistive effect
element 1a and between the lower electrode 6 and the
magnetoresistive effect element 1a. Each of the cap layer, the seed
layer, and the buffer layer may be made of Ru, Ta, Cu, or Cr or may
be formed of a stacked film including a Ru layer, a Ta layer, a Cu
layer, and a Cr layer. Each of the cap layer, the seed layer, and
the buffer layer preferably has a film thickness of about 2 nm to
10 nm.
[0052] When the magnetoresistive effect element 1a has a
rectangular shape (including a square shape) in plan view, the
magnetoresistive effect element 1a desirably has long sides of
about 100 nm or 100 nm or less. When the magnetoresistive effect
element 1a does not have a rectangular shape in plan view, the long
sides of a rectangle circumscribed around the plan view shape of
the magnetoresistive effect element 1a with a minimum area are
defined as the long sides of the magnetoresistive effect element
1a. When the long sides of the magnetoresistive effect element 1a
are short, for example, about 100 nm, the magnetization of the
magnetization free layer 4 is capable of having a single magnetic
domain to realize the spin torque resonance phenomenon with high
efficiency. The "plan view shape" means the shape of the
magnetoresistive effect element when the magnetoresistive effect
element is viewed from above a plane perpendicular to the stacking
direction of the respective layers composing the magnetoresistive
effect element.
[0053] The spin torque resonance phenomenon will now be
described.
[0054] Upon input of the high-frequency signal of a frequency equal
to the spin torque resonance frequency specific to the
magnetoresistive effect element 1a into the magnetoresistive effect
element 1a, the magnetization of the magnetization free layer 4
oscillates at the spin torque resonance frequency. This phenomenon
is called the spin torque resonance phenomenon. The element
resistance value of the magnetoresistive effect element 1a is
determined by the relative angle between the magnetization of the
magnetization fixed layer 2 and the magnetization of the
magnetization free layer 4. Accordingly, the resistance value of
the magnetoresistive effect element 1a in the spin torque resonance
varies with a fixed cycle with the oscillation of the magnetization
of the magnetization free layer 4. In other words, the
magnetoresistive effect element 1a is capable of being considered
as a resistor oscillation element the resistance value of which
varies with a fixed cycle at the spin torque resonance frequency.
In addition, upon input of the high-frequency signal of a frequency
equal to the spin torque resonance frequency into the
magnetoresistive effect element 1a while applying the direct
current flowing through the magnetoresistive effect element 1a in
the direction from the magnetization fixed layer 2 to the
magnetization free layer 4 to the magnetoresistive effect element
1a, the resistance value of the magnetoresistive effect element 1a
varies with a fixed cycle at the spin torque resonance frequency
out of phase with the input high-frequency signal by 180 degrees
and the impedance for the high-frequency signal is increased. In
other words, the magnetoresistive effect element 1a is capable of
being considered as a resistance element in which the impedance of
the high-frequency signal is increased at the spin torque resonance
frequency due to the spin torque resonance phenomenon.
[0055] The spin torque resonance frequency varies with the
effective magnetic field in the magnetization free layer 4. An
effective magnetic field H.sub.eff in the magnetization free layer
4 is represented by the following equation:
H.sub.eff=H.sub.E+H.sub.k+H.sub.D+H.sub.EX
where H.sub.E denotes an external magnetic field to be applied to
the magnetization free layer 4, H.sub.k denotes an anisotropy
magnetic field in the magnetization free layer 4, H.sub.D denotes a
demagnetizing field in the magnetization free layer 4, and H.sub.EX
denotes an exchange coupling magnetic field in the magnetization
free layer 4. The magnetic-field applying mechanism 12 is an
effective magnetic field setting mechanism that is capable of
setting the effective magnetic field H.sub.eff in the magnetization
free layer 4 by applying the magnetic field to the magnetoresistive
effect element 1a and applying the external magnetic field H.sub.E
to the magnetization free layer 4. The magnetic-field applying
mechanism 12, which is the effective magnetic field setting
mechanism, varies the effective magnetic field in the magnetization
free layer 4 by varying the magnetic field to be applied to the
magnetoresistive effect element 1a to enable the spin torque
resonance frequency of the magnetization free layer 4 to be varied.
As described above, varying the magnetic field to be applied to the
magnetoresistive effect element 1a varies the spin torque resonance
frequency.
[0056] The application of the direct current to the
magnetoresistive effect element 1a in the spin torque resonance
increases the spin torque to increase the amplitude of the
oscillating resistance value. The increase in the amplitude of the
oscillating resistance value increases the amount of change in
element impedance of the magnetoresistive effect element 1a.
Varying the current density of the applied direct current varies
the spin torque resonance frequency. Accordingly, the spin torque
resonance frequency of the magnetoresistive effect element 1a is
capable of being varied by varying the magnetic field from the
magnetic-field applying mechanism 12 or by varying the direct
current applied from the direct-current input terminal 11. The
current density of the direct current to be applied to the
magnetoresistive effect element 1a is preferably smaller than an
oscillation threshold current density of the magnetoresistive
effect element 1a. The oscillation threshold current density of the
magnetoresistive effect element means the current density at a
threshold value at which the magnetoresistive effect element
oscillates at start of precession of the magnetization of the
magnetization free layer in the magnetoresistive effect element at
a constant frequency and at a constant amplitude (the output (the
resistance value) of the magnetoresistive effect element is varied
at a constant frequency and at a constant amplitude) in response to
application of the direct current having a current density higher
than or equal to the oscillation threshold current density.
[0057] Due to the spin torque resonance phenomenon, the frequency
components that coincide with the spin torque resonance frequency
of the magnetoresistive effect element 1a or that are near the spin
torque resonance frequency of the magnetoresistive effect element
1a, among the high-frequency components of the high-frequency
signal input through the first port 9a, are cut off by the
magnetoresistive effect element 1a in a high impedance state and it
is difficult to supply the frequency components to the second port
9b. The magnetoresistive effect device 100 may function as a
high-frequency filter using the frequencies near the spin torque
resonance frequency as a cutoff frequency band in the above manner.
In other words, the magnetoresistive effect device 100 is a band
stop filter (band elimination filter).
[0058] FIG. 2 and FIG. 3 are graphs each illustrating the
relationship between the frequency of the high-frequency signal
input into the magnetoresistive effect device 100 and the
attenuation. Referring to FIG. 2 and FIG. 3, the vertical axis
represents attenuation and the horizontal axis represents
frequency. FIG. 2 is a graph when a constant magnetic field is
applied to the magnetoresistive effect element 1a. Referring to
FIG. 2, a plot line 100a1 represents the relationship between the
frequency of the high-frequency signal and the attenuation when the
direct current applied from the direct-current input terminal 11 to
the magnetoresistive effect element 1a has a value of Ia1 and a
plot line 100a2 represents the relationship between the frequency
of the high-frequency signal and the attenuation when the direct
current applied from the direct-current input terminal 11 to the
magnetoresistive effect element 1a has a value of Ia2. The
relationship between the applied direct current values is
Ia1<Ia2. FIG. 3 is a graph when constant direct current is
applied to the magnetoresistive effect element 1a. Referring to
FIG. 3, a plot line 100b1 represents the relationship between the
frequency of the high-frequency signal and the attenuation when the
magnetic field applied from the magnetic-field applying mechanism
12 to the magnetoresistive effect element 1a has a strength of Hb1
and a plot line 100b2 represents the relationship between the
frequency of the high-frequency signal and the attenuation when the
magnetic field applied from the magnetic-field applying mechanism
12 to the magnetoresistive effect element 1a has the strength of
Hb2. The relationship between the strengths of the magnetic fields
is Hb1<Hb2.
[0059] For example, when the value of the direct current applied
from the direct-current input terminal 11 to the magnetoresistive
effect element 1a is increased from Ia1 to Ia2, as illustrated in
FIG. 2, the amount of increase in element impedance at the
frequencies near the spin torque resonance frequency of the
magnetoresistive effect element 1a (the frequencies in the cutoff
frequency band) is increased with the variation in the current
value. As a result, the high-frequency signal output from the
second port 9b is further reduced to increase the attenuation (the
absolute value of the attenuation). Accordingly, the
magnetoresistive effect device 100 is capable of realizing a
high-frequency filter having a wide range of cut-off
characteristics and bandpass characteristics. In response to the
increase of the direct current value from Ia1 to Ia2, the spin
torque resonance frequency of the magnetoresistive effect element
1a is shifted from fa1 to fa2. In other words, the cutoff frequency
band is shifted toward low frequencies. Thus, the magnetoresistive
effect device 100 may function as a high-frequency filter capable
of varying the frequencies of the cutoff frequency band.
[0060] For example, when the strength of the magnetic field applied
from the magnetic-field applying mechanism 12 is increased from Hb1
to Hb2, as illustrated in FIG. 3, the spin torque resonance
frequency of the magnetoresistive effect element 1a is shifted from
fb1 to fb2. Specifically, the cutoff frequency band is shifted
toward high frequencies. The cutoff frequency band is capable of
being greatly shifted when the strength of the magnetic field (the
effective magnetic field H.sub.eff in the magnetization free layer
4) is varied, compared with the case in which the direct current
value is varied. In other words, the magnetoresistive effect device
100 may function as a high-frequency filter capable of varying the
frequencies of the cutoff frequency band.
[0061] The amplitude of the oscillating resistance value of the
magnetoresistive effect element 1a is reduced with an increase in
the external magnetic field H.sub.g to be applied to the
magnetoresistive effect element 1a (the effective magnetic field
H.sub.eff in the magnetization free layer 4). Accordingly, the
current density of the direct current to be applied to the
magnetoresistive effect element 1a is preferably increased with an
increase in the external magnetic field H.sub.E to be applied to
the magnetoresistive effect element 1a (the effective magnetic
field H.sub.eff in the magnetization free layer 4).
[0062] As described above, the magnetoresistive effect device 100
includes the magnetoresistive effect element 1a including the
magnetization fixed layer 2, the magnetization free layer 4, and
the spacer layer 3 arranged between the magnetization fixed layer 2
and the magnetization free layer 4; the first port 9a; the second
port 9b; the signal line 7; the inductor 10; and the direct-current
input terminal 11. The first port 9a, the magnetoresistive effect
element 1a, and the second port 9b are connected in series in this
order via the signal line 7. The inductor 10 is connected to the
signal line 7 between the magnetoresistive effect element 1a and
the second port 9b (one of the signal line 7 between the
magnetoresistive effect element 1a and the first port 9a and the
signal line 7 between the magnetoresistive effect element 1a and
the second port 9b) and is capable of being connected to the ground
8. The direct-current input terminal 11 is connected to the signal
line 7 between the magnetoresistive effect element 1a and the first
port 9a (the other of the signal line 7 between the
magnetoresistive effect element 1a and the first port 9a and the
signal line 7 between the magnetoresistive effect element 1a and
the second port 9b). A closed circuit including the
magnetoresistive effect element 1a, the signal line 7, the inductor
10, the ground 8, and the direct-current input terminal 11 is
capable of being formed. The magnetoresistive effect element 1a is
arranged so that the direct current supplied from the
direct-current input terminal 11 flows through the magnetoresistive
effect element 1a in the direction from the magnetization fixed
layer 2 to the magnetization free layer 4.
[0063] Accordingly, the input of the high-frequency signal from the
first port 9a to the magnetoresistive effect element 1a via the
signal line 7 enables the spin torque resonance to be induced in
the magnetoresistive effect element 1a. Due to the direct current
flowing through the magnetoresistive effect element 1a in the
direction from the magnetization fixed layer 2 to the magnetization
free layer 4 simultaneously with the spin torque resonance, the
magnetoresistive effect element 1a is capable of being considered
as an element the resistance value of which oscillates with a fixed
cycle at a frequency corresponding to the spin torque resonance
frequency out of phase with the high-frequency signal input through
the first port 9a by 180 degrees. With this effect, the element
impedance of the magnetoresistive effect element 1a at a frequency
equal to the spin torque resonance frequency is increased. The
series connection of the first port 9a, the magnetoresistive effect
element 1a, and the second port 9b in this order enables the
high-frequency signal to be passed at a non-resonant frequency at
which the magnetoresistive effect element 1a is in a low impedance
state and to be cut off at a resonant frequency at which the
magnetoresistive effect element 1a is in a high impedance state. In
other words, the magnetoresistive effect device 100 is capable of
having frequency characteristics as a high-frequency filter.
[0064] The inductor 10 connected to the signal line 7 and the
ground 8 does not pass the high-frequency signal but selectively
causes the direct current signal to flow to the ground.
Accordingly, the direct current supplied from the direct-current
input terminal 11 flows through the closed circuit including the
magnetoresistive effect element 1a, the signal line 7, the inductor
10, the ground 8, and the direct-current input terminal 11. The
closed circuit enables the direct current to be efficiently applied
to the magnetoresistive effect element 1a. In response to the
application of the direct current, the spin torque is increased and
the amplitude of the oscillating resistance value is increased in
the magnetoresistive effect element 1a. Since the increase in the
amplitude of the oscillating resistance value increases the amount
of change in element impedance of the magnetoresistive effect
element 1a, the magnetoresistive effect device 100 may function as
a high-frequency filter having a wide range of the cut-off
characteristics and the bandpass characteristics.
[0065] In order to increase the range of the cut-off
characteristics and the bandpass characteristics, the
magnetoresistive effect device 100 preferably has a configuration
in which the magnetization free layer 4 has the magnetic easy axis
in the plane normal direction and the magnetization fixed layer 2
has the magnetic easy axis in the in-plane direction.
[0066] In addition, since varying the direct current applied from
the direct-current input terminal 11 enables the spin torque
resonance frequency of the magnetoresistive effect element 1a to be
variably controlled, the magnetoresistive effect device 100 may
function as a variable frequency filter.
[0067] Furthermore, since the magnetoresistive effect device 100
includes the magnetic-field applying mechanism 12 serving as the
frequency setting mechanism capable of setting the spin torque
resonance frequency of the magnetoresistive effect element 1a, the
spin torque resonance frequency of the magnetoresistive effect
element 1a is capable of being set to an arbitrary value.
Accordingly, the magnetoresistive effect device 100 may function as
a filter having an arbitrary frequency band.
[0068] Furthermore, the magnetic-field applying mechanism 12 is the
effective magnetic field setting mechanism capable of setting the
effective magnetic field in the magnetization free layer 4 and is
capable of varying the spin torque resonance frequency of the
magnetoresistive effect element 1a by varying the effective
magnetic field in the magnetization free layer 4 in the
magnetoresistive effect device 100. Accordingly, the
magnetoresistive effect device 100 may function as the variable
frequency filter.
[0069] Various components may be added to the magnetoresistive
effect device 100 of the first embodiment described above. For
example, in order to prevent the direct current signal from flowing
into a high-frequency circuit connected to the first port 9a, a
capacitor for cutting off the direct current signal may be
connected in series to the signal line 7 between a connection
portion to the signal line 7 of the direct-current input terminal
11 and the first port 9a. Alternatively, in order to prevent the
direct current signal from flowing into a high-frequency circuit
connected to the second port 9b, a capacitor for cutting off the
direct current signal may be connected in series to the signal line
7 between a connection portion to the signal line 7 of the inductor
10 and the second port 9b.
Second Embodiment
[0070] FIG. 4 is a schematic cross-sectional view of a
magnetoresistive effect device 101 according to a second embodiment
of the present invention. Points different from the
magnetoresistive effect device 100 of the first embodiment in the
magnetoresistive effect device 101 will be mainly described and a
description of common points will be appropriately omitted herein.
The same reference numerals are used in the second embodiment to
identify the same components in the magnetoresistive effect device
100 of the first embodiment and a description of the common
components will be omitted herein. The magnetoresistive effect
device 101 includes two magnetoresistive effect elements 1a and 1b
each including the magnetization fixed layer 2, the spacer layer 3,
and the magnetization free layer 4, the upper electrode 5, the
lower electrode 6, the first port 9a, the second port 9b, the
signal line 7, the inductor 10, the direct-current input terminal
11, and the magnetic-field applying mechanism 12 serving as the
frequency setting mechanism. The magnetoresistive effect element 1a
is connected in parallel to the magnetoresistive effect element 1b
between the upper electrode 5 and the lower electrode 6. The first
port 9a, the magnetoresistive effect element 1a or the
magnetoresistive effect element 1b, and the second port 9b are
connected in series in this order via the signal line 7. The
magnetoresistive effect elements 1a and 1b have different spin
torque resonance frequencies from each other in a state in which
the same magnetic field and the direct current of the same current
density are applied. More specifically, although the
magnetoresistive effect elements 1a and 1b have the same film
structure and have rectangular shapes in plan view, the plan view
shape of the magnetoresistive effect element 1a is different from
the plan view shape of the magnetoresistive effect element 1a in
the aspect ratio. "The same film structure" means that the
magnetoresistive effect elements have the same material and the
same film thickness of each layer composing the magnetoresistive
effect elements and have the same stacking order of the layers.
"The plan view shape" means the shape of each of the
magnetoresistive effect elements when the magnetoresistive effect
element is viewed from above a plane perpendicular to the stacking
direction of the respective layers composing the magnetoresistive
effect element. "The aspect ratio" means the ratio of the length of
the long sides to the length of the short sides of a rectangle
circumscribed around the plan view shape of the magnetoresistive
effect element with a minimum area.
[0071] The inductor 10 is connected to the signal line 7 between
the magnetoresistive effect elements 1a and 1b, which are connected
in parallel to each other, and the second port 9b (one of the
signal line 7 between the magnetoresistive effect elements 1a and
1b and the first port 9a and the signal line 7 between the
magnetoresistive effect elements 1a and 1b and the second port 9b)
and is capable of being connected to the ground 8 via the reference
voltage terminal 20. The direct-current input terminal 11 is
connected to the signal line 7 between the magnetoresistive effect
elements 1a and 1b, which are connected in parallel to each other,
and the first port 9a (the other of the signal line 7 between the
magnetoresistive effect elements 1a and 1b and the first port 9a
and the signal line 7 between the magnetoresistive effect elements
1a and 1b and the second port 9b). In ether words, the
direct-current input terminal 11 is connected to the signal line 7
at the opposite side to the inductor 10 with the magnetoresistive
effect elements 1a and 1b in between the direct-current input
terminal 11 and the inductor 10. A closed circuit including the
magnetoresistive effect element 1a, the magnetoresistive effect
element 1b, the signal line 7, the inductor 10, the ground 8, and
the direct-current input terminal 11 is capable of being formed
when the magnetoresistive effect device 101 is connected to the
ground 8. More specifically, in the magnetoresistive effect device
101, the connection of the inductor 10 to the ground 8 via the
reference voltage terminal 20 and the connection of the
direct-current source 13 connected to the ground 8 to the
direct-current input terminal 11 enable the closed circuit
including the magnetoresistive effect element 1a, the
magnetoresistive effect element 1b, the signal line 7, the inductor
10, the ground 8, and the direct-current input terminal 11 to be
formed. The direct current supplied from the direct-current input
terminal 11 flows through the closed circuit and is applied to the
magnetoresistive effect element 1a and the magnetoresistive effect
element 1b. The magnetoresistive effect element 1a and the
magneto-resistive effect element 1b are arranged so that the direct
current supplied from the direct-current input terminal 11 flows
through the magnetoresistive effect element 1a and the
magnetoresistive effect element 1b in the direction from the
magnetization fixed layer 2 to the magnetization free layer 4.
[0072] The magnetization fixed layer 2 of the magnetoresistive
effect element 1a and the magnetization fixed layer 2 of the
magnetoresistive effect element 1b are connected to the same upper
electrode 5. The magnetization free layer 4 of the magnetoresistive
effect element 1a and the magnetization free layer 4 of the
magnetoresistive effect element 1b are connected to the same lower
electrode 6.
[0073] The magnetic-field applying mechanism 12 is disposed near
the magnetoresistive effect elements 1a and 1b and simultaneously
applies the same magnetic field to the magnetoresistive effect
elements 1a and 1b. The magnetic-field applying mechanism 12 varies
the effective magnetic fields in the magnetization free layers 4 in
the magnetoresistive effect elements 1a and 1b by varying the
magnetic fields to be applied to the magnetoresistive effect
elements 1a and 1b to enable the spin torque resonance frequencies
of the magnetoresistive effect elements 1a and 1b to be varied.
[0074] The film structures of the magnetoresistive effect elements
1a and 1b are the same as the film structure of the
magnetoresistive effect element 1a of the first embodiment. FIG. 5
is a top view of the magnetoresistive effect device 101. As
illustrated in FIG. 5, the magnetoresistive effect elements 1a and
1b have the same dimension Y.sub.0 in the Y direction, which is the
direction of the short sides of the plan view shapes of the
magnetoresistive effect elements 1a and 1b. However, a dimension Xa
in the X direction, which is the direction of the long sides of the
plan view shape of the magnetoresistive effect element 1a, is
different from a dimension Xb in the X direction, which is the
direction of the long sides of the plan view shape of the
magnetoresistive effect element 1b, and Xa<Xb. Accordingly, the
aspect ratio (Xb/Y.sub.0) of the plan view shape of the
magnetoresistive effect element 1b is higher than the aspect ratio
(Xa/Y.sub.0) of the plan view shape of the magnetoresistive effect
element 1a. In consideration of a state in which the same magnetic
field and the direct current of the same current density are
applied to each magnetoresistive effect element, the spin torque
resonance frequency of the magnetoresistive effect element is
increased with an increase in aspect ratio of the plan view shape
of the magnetoresistive effect element. As a result, a spin torque
resonance frequency fb of the magnetoresistive effect element 1b is
higher than a spin torque resonance frequency fa of the
magnetoresistive effect element 1a. Since differentiating the
aspect ratios of the plan view shapes of the multiple
magnetoresistive effect elements in the above manner enables the
spin torque resonance frequencies to be differentiated from each
other even when the magnetoresistive effect elements have the same
film structure, it is possible to manufacture the multiple
magnetoresistive effect elements having different spin torque
resonance frequencies from each other through the same film
formation process. In other words, since the multiple
magnetoresistive effect elements have the same film structure, it
is possible to collectively form the films of the layers composing
the multiple magnetoresistive effect elements.
[0075] Due to the spin torque resonance phenomenon, the frequency
components that coincide with the spin torque resonance frequency
of the magnetoresistive effect element 1a or the magnetoresistive
effect element 1b or that are near the spin torque resonance
frequency of the magnetoresistive effect element 1a or the
magnetoresistive effect element 1b, among the high-frequency
components of the high-frequency signal input through the first
port 9a, are cut off by the magnetoresistive effect element 1a and
the magnetoresistive effect element 1b, in which the combined
impedance is in a high impedance state and which are connected in
parallel to each other, and it is difficult to supply the frequency
components to the second port 9b. The magnetoresistive effect
device 101 may function as a high-frequency filter using the
frequencies near the spin torque resonance frequency of the
magnetoresistive effect element 1a or the magnetoresistive effect
element 1b as the cutoff frequency band.
[0076] FIG. 6 is a graph illustrating the relationship between the
frequency of the high-frequency signal input into the
magnetoresistive effect device 101 and the attenuation. Referring
to FIG. 6, the vertical axis represents attenuation and the
horizontal axis represents frequency. As illustrated in FIG. 6,
differentiating the aspect ratios of the plan view shapes of the
magnetoresistive effect elements 1a and 1b from each other so that
part of the frequencies near the spin torque resonance frequency fa
of the magnetoresistive effect element 1a (a cutoff frequency band
200a illustrated in FIG. 6) is overlapped with part of the
frequencies near the spin torque resonance frequency fb of the
magnetoresistive effect element 1b (a cutoff frequency band 200b
illustrated in FIG. 6) allows the magnetoresistive effect device
101 to have a cutoff frequency band (a cutoff frequency band 200
illustrated in FIG. 6) wider than that of the magnetoresistive
effect device 100 of the first embodiment, as illustrated in FIG.
6.
[0077] In addition, varying the direct current to be applied to the
magnetoresistive effect elements 1a and 1b or the strength of the
magnetic field to be applied from the magnetic-field applying
mechanism 12 to the magnetoresistive effect elements 1a and 1b
enables the bandwidth of the magnetoresistive effect device 101 to
be arbitrarily varied. Accordingly, the magnetoresistive effect
device 101 may function as a variable frequency filter capable of
arbitrarily varying the cutoff frequency band.
[0078] As described above, since the magnetoresistive effect
elements 1a and 1b having different spin torque resonance
frequencies from each other are connected in parallel to each other
in the magnetoresistive effect device 101, the impedance of the
multiple magnetoresistive effect elements near the multiple
frequencies equal to the spin torque resonance frequencies of the
respective magnetoresistive effect elements is increased and the
cutoff frequency band 200 having a certain width is provided. In
addition, varying the direct current or the magnetic field to be
applied to the magnetoresistive effect elements enables the
position of the cutoff frequency band to be varied. In other words,
the magnetoresistive effect device 101 may function as a variable
frequency filter capable of varying the position of the cutoff
frequency band.
[0079] Furthermore, since the plan view shapes of the multiple
magnetoresistive effect elements 1a and 1b have different aspect
ratios from each other in the magnetoresistive effect device 101,
it is possible to manufacture the multiple magnetoresistive effect
elements 1a and 1b having different spin torque resonance
frequencies from each other through the same process. Specifically,
since the multiple magnetoresistive effect elements 1a and 1b have
the same film structure in the magnetoresistive effect device 101,
it is possible to collectively form the films of the layers
composing the multiple magnetoresistive effect elements 1a and 1b,
thereby reducing the manufacturing cost.
[0080] Although the two magnetoresistive effect elements 1a and 1b
having different spin torque resonance frequencies from each other
are connected in parallel in the magnetoresistive effect device 101
of the second embodiment, three or more magnetoresistive effect
elements having different spin torque resonance frequencies from
each other may be connected in parallel. The width of the cutoff
frequency band is further increased in this case.
[0081] Although the two magnetoresistive effect elements 1a and 1b
have the same film structure in the magnetoresistive effect device
101 of the second embodiment, the multiple magnetoresistive effect
elements may have different film structures. In this case, the
different film structures may be used while the aspect ratios of
the plan view shapes of the multiple magnetoresistive effect
elements are made equal to each other to differentiate the spin
torque resonance frequencies of the multiple magnetoresistive
effect elements from each other.
[0082] Although the same magnetic field is simultaneously applied
to the magnetoresistive effect elements 1a and 1b by the
magnetic-field applying mechanism 12 in the magnetoresistive effect
device 101 of the second embodiment, magnetic-field applying
mechanisms for individually applying the magnetic fields to the
respective magnetoresistive effect elements may be provided.
Third Embodiment
[0083] FIG. 7 is a schematic cross-sectional view of a
magnetoresistive effect device 102 according to a third embodiment
of the present invention. Points different from the
magnetoresistive effect device 100 of the first embodiment in the
magnetoresistive effect device 102 will be mainly described and a
description of common points will be appropriately omitted herein.
The same reference numerals are used in the third embodiment to
identify the same components in the magnetoresistive effect device
100 of the first embodiment and a description of the common
components will be omitted herein. The magnetoresistive effect
device 102 includes two magnetoresistive effect elements 1a each
including the magnetization fixed layer 2, the spacer layer 3, and
the magnetization free layer 4, the upper electrode 5, the lower
electrode 6, the first port 9a, the second port 9b, the signal line
7, the inductor 10, the direct-current input terminal 11, and
magnetic-field applying mechanisms 12 serving as two frequency
setting mechanisms. The two magnetoresistive effect elements 1a
have the same configuration and are connected in parallel to each
other between the upper electrode 5 and the lower electrode 6. The
first port 9a, the two magnetoresistive effect elements 1a
connected in parallel to each other, and the second port 9b are
connected in series in this order via the signal line 7. The
respective magnetic-field applying mechanisms 12 apply individual
magnetic fields to the corresponding magnetoresistive effect
elements 1a. As described above, the magnetoresistive effect device
102 includes the two magnetic-field applying mechanisms 12 so as to
individually set the spin torque resonance frequencies of the two
respective magnetoresistive effect elements 1a. The inductor 10 is
connected to the signal line 7 between the two magnetoresistive
effect elements 1a, which are connected in parallel to each other,
and the second port 9b (one of the signal line 7 between the two
magnetoresistive effect elements 1a and the first port 9a and the
signal line 7 between the two magnetoresistive effect elements 1a
and the second port 9b) and is capable of being connected to the
ground 8 via the reference voltage terminal 20. The direct-current
input terminal 11 is connected to the signal line 7 between the two
magnetoresistive effect elements 1a, which are connected in
parallel to each other, and the first port 9a (the other of the
signal line 7 between the two magnetoresistive effect elements 1a
and the first port 9a and the signal line 7 between the two
magnetoresistive effect elements 1a and the second port 9b). In
other words, the direct-current input terminal 11 is connected to
the signal line 7 at the opposite side to the inductor 10 with the
two magnetoresistive effect elements 1a, which are connected in
parallel to each other, in between the direct-current input
terminal 11 and the inductor 10. A closed circuit including the two
magnetoresistive effect elements 1a, the signal line 7, the
inductor 10, the ground 8, and the direct-current input terminal 11
is capable of being formed when the magnetoresistive effect device
102 is connected to the ground 8. More specifically, in the
magnetoresistive effect device 102, the connection of the inductor
10 to the ground 8 via the reference voltage terminal 20 and the
connection of the direct-current source 13 connected to the ground
8 to the direct-current input terminal 11 enable the closed circuit
including the magnetoresistive effect elements 1a, the signal line
7, the inductor 10, the ground 8, and the direct-current input
terminal 11 to be formed. The direct current supplied from the
direct-current input terminal 11 flows through the closed circuit
and is applied to the two magnetoresistive effect elements 1a.
[0084] The magnetization fixed layers 2 of the two magnetoresistive
effect elements 1a are connected to the same upper electrode 5. The
magnetization free layers 4 of the two magnetoresistive effect
elements 1a are connected to the same lower electrode 6.
[0085] In the magnetoresistive effect device 102, the
high-frequency signal is supplied to the two magnetoresistive
effect elements 1a via the signal line 7 in a state in which the
magnetic fields are individually applied from the respective
magnetic-field applying mechanisms 12 to the corresponding
magnetoresistive effect elements 1a. For example, the strength of
the magnetic field to be applied to one of the magnetoresistive
effect elements 1a is made smaller than the strength of the
magnetic field to be applied to the other of the magnetoresistive
effect elements 1a. The spin torque resonance frequencies of the
two magnetoresistive effect elements 1a are different from each
other in this case.
[0086] Due to the spin torque resonance phenomenon, the frequency
components that coincide with the spin torque resonance frequency
of either of the two magnetoresistive effect elements 1a or that
are near the spin torque resonance frequency of either of the two
magnetoresistive effect elements 1a, among the high-frequency
components of the high-frequency signal input through the first
port 9a, are out off by the two magnetoresistive effect elements
1a, in which the combined impedance is in a high impedance state
and which are connected in parallel to each other, and it is
difficult to supply the frequency components to the second port 9b.
The magnetoresistive effect device 102 may function as a
high-frequency filter using the frequencies near the spin torque
resonance frequency of either of the two magnetoresistive effect
elements 1a as the cutoff frequency band.
[0087] FIG. 8 is a graph illustrating the relationship between the
frequency of the high-frequency signal input into the
magnetoresistive effect device 102 and the attenuation. Referring
to FIG. 8, the vertical axis represents attenuation and the
horizontal axis represents frequency. For example, as illustrated
in FIG. 8, when the magnetic field to be applied to one of the
magnetoresistive effect elements 1a is made smaller than the
magnetic field to be applied to the other of the magnetoresistive
effect elements 1a, f1<f2 where f1 denotes the spin torque
resonance frequency of one of the magnetoresistive effect elements
1a and f2 denotes the spin torque resonance frequency of the other
of the magnetoresistive effect elements 1a. Accordingly, as
illustrated in FIG. 8, adjusting the strength of the magnetic field
to be applied from each of the magnetic-field applying mechanisms
12 to the corresponding magnetoresistive effect element 1a so that
part of the frequencies near the spin torque resonance frequency f1
of one of the magnetoresistive effect elements 1a (a cutoff
frequency band 300a illustrated in FIG. 8) is overlapped with part
of the frequencies near the spin torque resonance frequency f2 of
the other of the magnetoresistive effect elements 1a (a cutoff
frequency band 300b illustrated in FIG. 8) allows the
magnetoresistive effect device 102 to have a cutoff frequency band
(a cutoff frequency band 300 illustrated in FIG. 8) wider than that
of the magnetoresistive effect device 100 of the first embodiment,
as illustrated in FIG. 8.
[0088] In addition, varying the direct current to be applied to
each of the magnetoresistive effect elements 1a or the strength of
the magnetic field to be applied from each of the magnetic-field
applying mechanisms 12 to the corresponding magnetoresistive effect
element 1a enables the bandwidth of the magnetoresistive effect
device 102 to be arbitrarily varied. Accordingly, the
magnetoresistive effect device 102 may function as a variable
frequency filter capable of arbitrarily varying the cutoff
frequency band.
[0089] As described above, since the magnetoresistive effect device
102 includes the multiple magnetic-field applying mechanisms 12
serving as the frequency setting mechanisms so as to individually
set the spin torque resonance frequencies of the respective
multiple magnetoresistive effect elements 1a, the magnetoresistive
effect device 102 is capable of individually controlling the spin
torque resonance frequencies of the respective magnetoresistive
effect elements 1a. In addition, since the multiple
magnetoresistive effect elements 1a are connected in parallel to
each other, the impedance of the multiple magnetoresistive effect
elements near the multiple frequencies equal to the spin torque
resonance frequencies of the respective magnetoresistive effect
elements 1a is increased and the cutoff frequency band 300 having a
certain width is provided. Furthermore, varying the direct current
or the magnetic field to be applied to each of the magnetoresistive
effect elements 1a enables the bandwidth of the magnetoresistive
effect device 102 to be arbitrarily varied. Accordingly, the
magnetoresistive effect device 102 may function as a variable
frequency filter capable of arbitrarily varying the cutoff
frequency band.
[0090] Furthermore, although the two magnetoresistive effect
elements 1a are connected in parallel to each other and the two
frequency setting mechanisms (the two magnetic-field applying
mechanisms 12) are provided so as to individually set the spin
torque resonance frequencies of the respective magnetoresistive
effect elements 1a in the magnetoresistive effect device 102 of the
third embodiment, three or more magnetoresistive effect elements 1a
may be connected in parallel to each other and three or more
frequency setting mechanisms (three or more magnetic-field applying
mechanisms 12) may be provided so as to individually set the spin
torque resonance frequencies of the respective magnetoresistive
effect elements 1a. The width of the cutoff frequency band is
further increased in this case.
[0091] Furthermore, although the two magnetoresistive effect
elements 1a have the same configuration in the magnetoresistive
effect device 102 of the third embodiment, the multiple
magnetoresistive effect elements may have different
configurations.
Fourth Embodiment
[0092] FIG. 9 is a schematic cross-sectional view of a
magnetoresistive effect device 103 according to a fourth embodiment
of the present invention. Points different from the
magnetoresistive effect device 100 of the first embodiment in the
magnetoresistive effect device 103 will be mainly described and a
description of common points will be appropriately omitted herein.
The same reference numerals are used in the fourth embodiment to
identify the same components in the magnetoresistive effect device
100 of the first embodiment and a description of the common
components Will be omitted herein. The magnetoresistive effect
device 103 includes the two magnetoresistive effect elements 1a and
1b each including the magnetization fixed layer 2, the spacer layer
3, and the magnetization free layer 4, upper electrodes 5a and 5b,
lower electrodes 6a and 6b, the first port 9a, the second port 9b,
the signal line 7, the inductor 10, the direct-current input
terminal 11, and the magnetic-field applying mechanism 12 serving
as the frequency setting mechanism. The upper electrode 5a and the
lower electrode 6a are arranged so as to sandwich the
magnetoresistive effect element 1a therebetween and the upper
electrode 5b and the lower electrode 6b are arranged so as to
sandwich the magnetoresistive effect element 1b therebetween. The
magnetoresistive effect element 1a is connected in series to the
magnetoresistive effect element 1b. The first port 9a, the
magnetoresistive effect element 1a, the magnetoresistive effect
element 1b, and the second port 9b are connected in series in this
order via the signal line 7. The magnetoresistive effect elements
1a and 1b have different spin torque resonance frequencies from
each other in a state in which the same magnetic field and the
direct current of the same current density are applied. More
specifically, although the magnetoresistive effect elements 1a and
1b have the same film structure and have rectangular shapes in plan
view, the plan view shape of the magnetoresistive effect element 1a
is different from the plan view shape of the magnetoresistive
effect element 1a in the aspect ratio. "The same film structure"
means that the magnetoresistive effect elements 1a and 1b have the
same material and the same film thickness of each layer composing
the magnetoresistive effect elements and have the same stacking
order of the layers. "The plan view shape" means the shape of each
of the magnetoresistive effect elements when the magnetoresistive
effect element is viewed from above a plane perpendicular to the
stacking direction of the respective layers composing the
magnetoresistive effect element. "The aspect ratio" means the ratio
or the length of the long sides to the length of the short sides of
a rectangle circumscribed around the plan view shape of the
magnetoresistive effect element with a minimum area.
[0093] The inductor 10 is connected to the signal line 7 between
the magnetoresistive effect element 1b and the second port 9b (one
of the signal line 7 between the magnetoresistive effect elements
1a and 1b and the first port 9a and the signal line 7 between the
magnetoresistive effect elements 1a and 1b and the second port 9b)
and is capable of being connected to the ground 8 via the reference
voltage terminal 20. The direct-current input terminal 11 is
connected to the signal line 7 between the magnetoresistive effect
elements 1a and 1b, which are connected in series to each other,
and the first port 9a (the other of the signal line 7 between the
magnetoresistive effect elements 1a and 1b and the first port 9a
and the signal line 7 between the magnetoresistive effect elements
1a and 1b and the second port 9b). In other words, the
direct-current input terminal 11 is connected to the signal line 7
at the opposite side to the inductor 10 with the magnetoresistive
effect elements 1a and 1b in between the direct-current input
terminal 11 and the inductor 10. A closed circuit including the
magnetoresistive effect element 1a, the magnetoresistive effect
element 1b, the signal line 7, the inductor 10, the ground 8, and
the direct-current input terminal 11 is capable of being formed
when the magnetoresistive effect device 103 is connected to the
ground 8. More specifically, in the magnetoresistive effect device
103, the connection of the inductor 10 to the ground 8 via the
reference voltage terminal 20 and the connection of the
direct-current source 13 connected to the ground 8 to the
direct-current input terminal 11 enable the closed circuit
including the magnetoresistive effect element 1a, the
magnetoresistive effect element 1b, the signal line 7, the inductor
10, the ground 8, and the direct-current input terminal 11 to be
formed. The direct current supplied from the direct-current input
terminal 11 flows through the closed circuit and is applied to the
magnetoresistive effect element 1a and the magnetoresistive effect
element 1b. The magnetoresistive effect element 1a and the
magnetoresistive effect element 1b are arranged so that the direct
current supplied from the direct-current input terminal 11 flows
through the magnetoresistive effect element 1a and the
magnetoresistive effect element 1b in the direction from the
magnetization fixed layer 2 to the magnetization free layer 4.
[0094] The lower electrode 6a to which the magnetization free layer
4 of the magnetoresistive effect element 1a is connected is
electrically connected to the upper electrode 5b to which the
magnetization fixed layer 2 of the magnetoresistive effect element
1b is connected. The magnetoresistive effect elements 1a and 1b are
connected in series to each other.
[0095] The magnetic-field applying mechanism 12 is disposed near
the magnetoresistive effect elements 1a and 1b and simultaneously
applies the same magnetic field to the magnetoresistive effect
elements 1a and 1b. The magnetic-field applying mechanism 12 varies
the effective magnetic fields in the magnetization free layers 4 in
the magnetoresistive effect elements 1a and 1b by varying the
magnetic fields to be applied to the magnetoresistive effect
elements 1a and 1b to enable the spin torque resonance frequencies
of the magnetoresistive effect elements 1a and 1b to be varied.
[0096] The film structures of the magnetoresistive effect elements
1a and 1b are the same as the film structure of the
magnetoresistive effect element 1a of the first embodiment. FIG. 10
is a top view of the magnetoresistive effect device 103. As
illustrated in FIG. 10, the magnetoresistive effect elements 1a and
1b have the same dimension Y.sub.0 in the Y direction, which is the
direction of the short sides of the plan view shapes of the
magnetoresistive effect elements 1a and 1b. However, the dimension
Xa in the X direction, which is the direction of the long sides of
the plan view shape of the magnetoresistive effect element 1a, is
different from the dimension Xb in the X direction, which is the
direction of the long sides of the plan view shape of the
magnetoresistive effect element 1b, and Xa<Xb. Accordingly, the
aspect ratio (Xb/Y.sub.0) of the plan view shape of the
magnetoresistive effect element 1b is higher than the aspect ratio
(Xa/Y.sub.0) of the plan view shape of the magnetoresistive effect
element 1a. In consideration of the state in which the same
magnetic field and the direct current of the same current density
are applied to each magnetoresistive offset element, the spin
torque resonance frequency of the magnetoresistive effect element
is increased with an increase in aspect ratio of the plan view
shape of the magnetoresistive effect element. As a result, the spin
torque resonance frequency fb of the magnetoresistive effect
element 1b is higher than the spin torque resonance frequency fa of
the magnetoresistive effect element 1a. Since differentiating the
aspect ratios of the plan view shapes of the multiple
magnetoresistive effect elements in the above manner enables the
spin torque resonance frequencies to be differentiated from each
other even when the magnetoresistive effect elements have the same
film structure, it is possible to manufacture the multiple
magnetoresistive effect elements having different spin torque
resonance frequencies from each other through the same film
formation process. In other words, since the multiple
magnetoresistive effect elements have the same film structure, it
is possible to collectively form the films of the layers composing
the multiple magnetoresistive effect elements. In addition, in the
magnetoresistive effect device 103, since the magnetoresistive
effect elements 1a and 1b are connected in series to each other and
the area of the cross section of the magnetoresistive effect
element 1a in a direction perpendicular to the direction in which
the direct current flows is smaller than the area of the cross
section of the magnetoresistive effect element 1b in the direction,
the current density of the direct current applied to the
magnetoresistive effect element 1a is higher than that of the
direct current applied to the magnetoresistive effect element 1b.
Accordingly, when the spin torque resonance frequency of the
magnetoresistive effect element is decreased with an increase in
the current density of the applied direct current or when the
effect of the difference in the aspect ratio of the plan view shape
of the magnetoresistive effect element on the spin torque resonance
frequency of the magnetoresistive effect element is greater than
the effect of the difference in the current density of the applied
direct current on the spin torque resonance frequency of the
magnetoresistive effect element, the plan view shape of the
magnetoresistive effect element 1a is different from the plan view
shape of the magnetoresistive effect element 1b in the aspect ratio
and fa<fb.
[0097] Due to the spin torque resonance phenomenon, the frequency
components that coincide with the spin torque resonance frequency
of the magnetoresistive effect element 1a or the magnetoresistive
effect element 1b or that are near the spin torque resonance
frequency of the magnetoresistive effect element 1a or the
magnetoresistive effect element 1b, among the high-frequency
components of the high-frequency signal input through the first
port 9a, are cut off by the magnetoresistive effect element 1a and
the magnetoresistive effect element 1b, in which the combined
impedance is in a high impedance state and which are connected in
series to each other, and it is difficult to supply the frequency
components to the second port 9b. The magnetoresistive effect
device 103 may function as a high-frequency filter using the
frequencies near the spin torque resonance frequency of the
magnetoresistive effect element 1a or the magnetoresistive effect
element 1b as the cutoff frequency band.
[0098] FIG. 11 is a graph illustrating the relationship between the
frequency of the high-frequency signal input into the
magnetoresistive effect device 103 and the attenuation. Referring
to FIG. 11, the vertical axis represents attenuation and the
horizontal axis represents frequency. As illustrated in FIG. 11,
differentiating the aspect ratios of the plan view shapes of the
magnetoresistive effect elements 1a and 1b from each other so that
part of the frequencies near the spin torque resonance frequency fa
of the magnetoresistive effect element 1a (a cutoff frequency band
400a illustrated in FIG. 11) is overlapped with part of the
frequencies near the spin torque resonance frequency fb of the
magnetoresistive effect element 1b (a cutoff frequency band 400b
illustrated in FIG. 11) allows the magnetoresistive effect device
103 to have a cutoff frequency band (a cutoff frequency band 400
illustrated in FIG. 11) wider than that of the magnetoresistive
effect device 100 of the first embodiment, as illustrated in FIG.
11.
[0099] In addition, varying the direct current to be applied to the
magnetoresistive effect elements 1a and 1b or the strength of the
magnetic field to be applied from the magnetic-field applying
mechanism 12 to the magnetoresistive effect elements 1a and 1b
enables the bandwidth of the magnetoresistive effect device 103 to
be arbitrarily varied. Accordingly, the magnetoresistive effect
device 103 may function as a variable frequency filter capable of
arbitrarily varying the cutoff frequency band.
[0100] As described above, since the multiple magnetoresistive
effect elements 1a and 1b having different spin torque resonance
frequencies from each other are connected in series to each other
in the magnetoresistive effect device 103, the impedance of the
multiple magnetoresistive effect elements near the multiple
frequencies equal to the spin torque resonance frequencies of the
respective magnetoresistive effect elements is increased and the
cutoff frequency band 400 having a certain width is provided. In
addition, varying the direct current or the magnetic field to be
applied to the magnetoresistive effect elements enables the
position of the cutoff frequency band to be varied. In other words,
the magnetoresistive effect device 103 may function as a variable
frequency filter capable of varying the position of the cutoff
frequency band.
[0101] Furthermore, since the plan view shapes of the multiple
magnetoresistive effect elements 1a and 1b have different aspect
ratios from each other in the magnetoresistive effect device 103,
it is possible to manufacture the multiple magnetoresistive effect
elements 1a and 1b having different spin torque resonance
frequencies from each other through the same process. Specifically,
since the multiple magnetoresistive effect elements 1a and 1b have
the same film structure in the magnetoresistive effect device 103,
it is possible to collectively form the films of the layers
composing the multiple magnetoresistive effect elements 1a and 1b,
thereby reducing the manufacturing cost.
[0102] Although the two magnetoresistive effect elements 1a and 1b
having different spin torque resonance frequencies from each other
are connected in series to each other in the magnetoresistive
effect device 103 of the fourth embodiment, three or more
magnetoresistive effect elements having different spin torque
resonance frequencies from each other may be connected in series to
each other. The width of the cutoff frequency band is further
increased in this case.
[0103] Although the two magnetoresistive effect elements 1a and 1b
have the same film structure in the magnetoresistive effect device
103 of the fourth embodiment, the multiple magnetoresistive effect
elements may have different film structures. In this case, the
different film structures may be used while the aspect ratios of
the plan view shapes of the multiple magnetoresistive effect
elements are made equal to each other to differentiate the spin
torque resonance frequencies of the multiple magnetoresistive
effect elements from each other.
[0104] Although the same magnetic field is simultaneously applied
to the magnetoresistive effect elements 1a and 1b by the
magnetic-field applying mechanism 12 in the magnetoresistive effect
device 103 of the fourth embodiment, magnetic-field applying
mechanisms for individually applying the magnetic fields to the
respective magnetoresistive effect elements may be provided, as in
the third embodiment.
Fifth Embodiment
[0105] FIG. 12 is a schematic cross-sectional view of a
magnetoresistive effect device 104 according to a fifth embodiment
of the present invention. Points different from the
magnetoresistive effect device 100 of the first embodiment in the
magnetoresistive effect device 104 will be mainly described and a
description of common points will be appropriately omitted herein.
The same reference numerals are used in the fifth embodiment to
identify the same components in the magnetoresistive effect device
100 of the first embodiment and a description of the common
components will be omitted herein. The magnetoresistive effect
device 104 includes the two magnetoresistive effect elements 1a
each including the magnetization fixed layer 2, the spacer layer 3,
and the magnetization free layer 4, the upper electrodes 5a and 5b,
the lower electrodes 6a and 6b, the first port 9a, the second port
9b, the signal line 7, the inductor 10, the direct-current input
terminal 11, and the magnetic-field applying mechanisms 12 serving
as the two frequency setting mechanisms. The two magnetoresistive
effect elements 1a have the same configuration. The upper electrode
5a and the lower electrode 6a are arranged so as to sandwich one of
the magnetoresistive effect elements 1a therebetween and the upper
electrode 5b and the lower electrode 6b are arranged so as to
sandwich the other of the magnetoresistive effect elements 1a
therebetween. The two magnetoresistive effect elements 1a are
connected in series to each other. The first port 9a, the
magnetoresistive effect elements 1a, and the second port 9b are
connected in series in this order via the signal line 7. The
respective magnetic-field applying mechanisms 12 apply individual
magnetic fields to the corresponding magnetoresistive effect
elements 1a. As described above, the magnetoresistive effect device
104 includes the two magnetic-field applying mechanisms 12 so as to
individually setting the spin torque resonance frequencies of the
two respective magnetoresistive effect elements 1a. The inductor 10
is connected to the signal line 7 between the two magnetoresistive
effect elements 1a, which are connected in series to each other,
and the second port 9b (one of the signal line 7 between the two
magnetoresistive effect elements 1a and the first port 9a and the
signal line 7 between the two magnetoresistive effect elements 1a
and the second port 9b) and is capable of being connected to the
ground 8 via the reference voltage terminal 20. The direct-current
input terminal 11 is connected to the signal line 7 between the two
magnetoresistive effect elements 1a, which are connected in series
to each other, and the first port 9a (the other of the signal line
7 between the two magnetoresistive effect elements 1a and the first
port 9a and the signal line 7 between the two magnetoresistive
effect elements 1a and the second port 9b). In other words, the
direct-current input terminal 11 is connected to the signal line 7
at the opposite side to the inductor 10 with the two
magnetoresistive effect elements 1a, which are connected in series
to each other, in between the direct-current input terminal 11 and
the inductor 10. A closed circuit including the two
magnetoresistive effect elements 1a, the signal line 7, the
inductor 10, the ground 8, and the direct-current input terminal 11
is capable of being formed when the magnetoresistive effect device
104 is connected to the ground 8. More specifically, in the
magnetoresistive effect device 104, the connection of the inductor
10 to the ground 8 via the reference voltage terminal 20 and the
connection of the direct-current source 13 connected to the ground
8 to the direct-current input terminal 11 enable the closed circuit
including the two magnetoresistive effect elements 1a, which are
connected in series to each other, the signal line 7, the inductor
10, the ground 8, and the direct-current input terminal 11 to be
formed. The direct current supplied from the direct-current input
terminal 11 flows through the closed circuit and is applied to the
two magnetoresistive effect elements 1a.
[0106] The lower electrode 6a to which the magnetization free layer
4 of one of the magnetoresistive effect elements 1a is connected is
electrically connected to the upper electrode 5b to which the
magnetization fixed layer 2 of the other of the magnetoresistive
effect elements 1a is connected. The two magnetoresistive effect
elements 1a are connected in series to each other.
[0107] In the magnetoresistive effect device 104, the
high-frequency signal is supplied to the two magnetoresistive
effect elements 1a via the signal line 7 in a state in which the
magnetic fields are individually applied from the respective
magnetic-field applying mechanisms 12 to the corresponding
magnetoresistive effect elements 1a. For example, the strength of
the magnetic field to be applied to one of the magnetoresistive
effect elements 1a is made smaller than the strength of the
magnetic field to be applied to the other of the magnetoresistive
effect elements 1a. The spin torque resonance frequencies of the
two magnetoresistive effect elements 1a are different from each in
this case.
[0108] Due to the spin torque resonance phenomenon, the frequency
components that coincide with the spin torque resonance frequency
of either of the two magnetoresistive effect elements 1a or that
are near the spin torque resonance frequency of either of the two
magnetoresistive elements 1a, among the high-frequency components
of the high-frequency signal input through the first port 9a, are
cut off by the two magnetoresistive effect elements 1a in which the
combined impedance is in a high impedance state and which are
connected in series to each other, and it is difficult to supply
the frequency components to the second port 9b. The
magnetoresistive effect device 104 may function as a high-frequency
filter using the frequencies near the spin torque resonance
frequency of either of the two magnetoresistive effect elements 1a
as the cutoff frequency band.
[0109] FIG. 13 is a graph illustrating the relationship between the
frequency of the high-frequency signal input into the
magnetoresistive effect device 104 and the attenuation. Referring
to FIG. 13, the vertical axis represents attenuation and the
horizontal axis represents frequency. For example, as illustrated
in FIG. 13, when the magnetic field to be applied to one of the
magnetoresistive effect elements 1a is made smaller than the
magnetic field to be applied to the other of the magnetoresistive
effect elements 1a, f1<f2 where f1 denotes the spin torque
resonance frequency of one of the magnetoresistive effect elements
1a and f2 denotes the spin torque resonance frequency of the other
of the magnetoresistive effect elements 1a. Accordingly, as
illustrated in FIG. 13, adjusting the strength of the magnetic
field to be applied from each of the magnetic-field applying
mechanisms 12 to the corresponding magnetoresistive effect element
1a so that part of the frequencies near the spin torque resonance
frequency f1 of one of the magnetoresistive effect elements 1a (a
cutoff frequency band 500a illustrated in FIG. 13) is overlapped
with part of the frequencies near the spin torque resonance
frequency f2 of the other of the magnetoresistive effect elements
1a (a cutoff frequency band 500b illustrated in FIG. 13) allows the
magnetoresistive effect device 104 to have a cutoff frequency band
(a cutoff frequency band 500 illustrated in FIG. 13) wider than
that of the magnetoresistive effect device 100 of the first
embodiment, as illustrated in FIG. 13.
[0110] In addition, varying the direct current to be applied to
each of the magnetoresistive effect elements 1a or the strength of
the magnetic field to be applied from each of the magnetic-field
applying mechanisms 12 to the corresponding magnetoresistive effect
element 1a enables the bandwidth of the magnetoresistive effect
device 104 to be arbitrarily varied. Accordingly, the
magnetoresistive effect device 104 may function as a variable
frequency filter capable of arbitrarily varying the cutoff
frequency band.
[0111] As described above, since the magnetoresistive effect device
104 includes the multiple magnetic-field applying mechanisms 12
serving as the frequency setting mechanisms so as to individually
set the spin torque resonance frequencies of the multiple
magnetoresistive effect elements 1a, the magnetoresistive effect
device 104 is capable of individually controlling the spin torque
resonance frequencies of the respective magnetoresistive effect
elements 1a. In addition, since the multiple magnetoresistive
effect elements 1a are connected in series to each other, the
impedance of the multiple magnetoresistive effect elements near the
multiple frequencies equal to the spin torque resonance frequencies
of the respective magnetoresistive effect elements 1a is increased
and the cutoff frequency band 500 having a certain width is
provided. Furthermore, varying the direct current or the magnetic
field to be applied to each of the magnetoresistive effect elements
1a enables the bandwidth of the magnetoresistive effect device 104
to be arbitrarily varied. Accordingly, the magnetoresistive effect
device 104 may function as a variable frequency filter capable of
arbitrarily varying the cutoff frequency band.
[0112] Furthermore, although the two magnetoresistive effect
elements 1a are connected in series to each other and the two
frequency setting mechanisms (the two magnetic-field applying
mechanisms 12) are provided so as to individually set the spin
torque resonance frequencies of the respective magnetoresistive
effect elements 1a in the magnetoresistive effect device 104 of the
fifth embodiment, three or more magnetoresistive effect elements 1a
may be connected in series to each other and three or more
frequency setting mechanisms (three or more magnetic-field applying
mechanisms 12) may be provided so as to individually set the spin
torque resonance frequencies of the respective magnetoresistive
effect elements 1a. The width of the cutoff frequency band is
further increased in this case.
[0113] Furthermore, although the two magnetoresistive effect
elements 1a have the same configuration in the magnetoresistive
effect device 104 of the fifth embodiment, the multiple
magnetoresistive effect elements may have different
configurations.
[0114] Although the embodiments of the present invention have been
described above, it will be clear that the present invention is not
limited to these specific examples and embodiments and that many
changes and modified embodiments will be obvious to those skilled
in the art. For example, although the examples are described in the
first to fifth embodiments in which the inductor 10 is connected to
the signal line 7 between the magnetoresistive effect element 1a
(1b) and the second port 9b and the direct-current input terminal
11 is connected to the signal line 7 between the magnetoresistive
effect element 1a (1b) and the first port 9a, the inductor 10 may
be connected to the signal line 7 between the magnetoresistive
effect element 1a (1b) and the first port 9a and the direct-current
input terminal 11 may be connected to the signal line between the
magnetoresistive effect element 1a (1b) and the second port 9b.
[0115] Although the examples are described in the first to fifth
embodiments in which the inductor 10 is used, a resistance element
may be used, instead of the inductor 10. In this case, the
resistance element is connected between the signal line 7 and the
ground 8 and has a function to cut off the high-frequency
components of the current with its resistance component. The
resistance element may be a chip resistor or a resistor composed of
a pattern line. The resistance value of the resistance element is
preferably higher than the characteristic impedance of the signal
line 7. For example, when the characteristic impedance of the
signal line 7 is 50.OMEGA., high-frequency power of 45% is capable
of being cut with the resistance element if the resistance value of
the resistance element is 50.OMEGA. and high-frequency power of 90%
is capable of being cut with the resistance element if the
resistance value of the resistance element is 500.OMEGA.. The use
of the resistance element enables the direct current applied from
the direct-current input terminal 11 to flow through a closed
circuit including the magnetoresistive effect element 1a (1b), the
signal line 7, the resistance element, the ground 8, and the
direct-current input terminal 11 without degrading the
characteristics of the high-frequency signal passing through the
magnetoresistive effect element 1a (1b).
[0116] When the resistance element is used, instead of the inductor
10, it is preferable to connect a capacitor for cutting off the
direct current signal in series to the signal line 7 between a
connection portion to the signal line 7 of the direct-current input
terminal 11 (or the resistance element) and the first port 9a and
to connect a capacitor for cutting off the direct current signal in
series to the signal line 7 between a connection portion to the
signal line 7 of the resistance element (or the direct-current
input terminal 11) and the second port 9b in order to cause the
direct current applied from the direct-current input terminal 11 to
efficiently flow through the closed circuit including the
magnetoresistive effect element 1a (1b), the signal line 7, the
resistance element, the ground 8, and the direct-current input
terminal 11.
[0117] Although the examples are described in the first to fifth
embodiments in which the magnetoresistive effect device 100 (101,
102, 103, and 104) include the magnetic-field applying mechanism 12
as the frequency setting mechanism (the effective magnetic field
setting mechanism), the frequency setting mechanism (the effective
magnetic field setting mechanism) may be realized in the following
manner. For example, the anisotropy magnetic field H.sub.k in the
magnetization free layer may be varied by applying an electric
field to the magnetoresistive effect element and varying the
electric field to vary the effective magnetic field in the
magnetization free layer, thereby varying the spin torque resonance
frequency of the magnetoresistive effect element. In this case, a
mechanism to apply the electric field to the magnetoresistive
effect element serves as the frequency setting mechanism (the
effective magnetic field setting mechanism). Alternatively, the
anisotropy magnetic field H.sub.k in the magnetization free layer
may be varied by providing a piezoelectric body near the
magnetization free layer, applying the electric field to the
piezoelectric body to deform the piezoelectric body, and deforming
the magnetization free layer to vary the effective magnetic field
in the magnetization free layer, thereby varying the spin torque
resonance frequency of the magnetoresistive effect element. In this
case, a mechanism to apply the electric field to the piezoelectric
body and the piezoelectric body serve as the frequency setting
mechanism (the effective magnetic field setting mechanism).
Alternatively, the exchange coupling magnetic field H.sub.EX in the
magnetization free layer may be varied by providing a control film
that has an electromagnetic effect and that is made of an
antiferromagnetic material or a ferromagnetic material so as to be
magnetically coupled to the magnetization free layer, applying the
magnetic field and the electric field to the control film, and
varying at least one of the magnetic field and the electric field
to be applied to the control film to vary the effective magnetic
field in the magnetization free layer, thereby varying the spin
torque resonance frequency of the magnetoresistive effect element.
In this case, a mechanism to apply the magnetic field to the
control film, a mechanism to apply the electric field to the
control film, and the control film serve as the frequency setting
mechanism (the effective magnetic field setting mechanism).
[0118] If the spin torque resonance frequency of each
magnetoresistive effect element has a desired value even when the
frequency setting mechanism is not provided (the magnetic field is
not applied from the magnetic-field applying mechanism 12), the
frequency setting mechanism (the magnetic-field applying mechanism
12) may not be provided.
* * * * *